Saturday, December 17, 2011

We live in dynamic times. Buzzwords such as cloud computing, elastic scale, reliability and their synonyms are taking more and more space in our daily life. People (developers) want to move to the cloud. They are often confused by all the new terms. In this part 1 of [we-will-see-at-the-end-how-many] articles I will try to explain with non-geeky words the Windows Azure terms.

First of all, what is Cloud Computing before all? This is when Computing power (namely CPU, RAM, Storage, Networking) is delivered as a service via a network (usually internet), and not as a product (a server that we buy).

Cloud computing is a marketing term for technologies that provide computation, software, data access, and storage services that do not require end-user knowledge of the physical location and configuration of the system that delivers the services. A parallel to this concept can be drawn with the electricity grid, wherein end-users consume power without needing to understand the component devices or infrastructure required to provide the service.

Windows Azure Guest OS? When we talk about cloud computing, inevitably we talk about virtualization. Virtualization at very big degree. And when we talk about virtualization, we have a Host OS and Guest OS. When we talk about Windows Azure OS, we talk about Windows Azure Guest OS. This is the operating system that is installed on the Virtual Machines that run in the cloud. Windows Azure Guest OS has 2 families – OS Family 1 and OS Family 2. Windows Azure Guest OS Family 1 is based on Windows Server 2008 SP 1 x64, and Family 2 is based on Windows Server 2008 R2. All and any guest OS is 64 bits. You can get the full list of Windows Azure Guest OS here.

Windows Azure Cloud Service, or Hosted Service. The Hosted Service is the essence of your Cloud application:

A hosted service in Windows Azure consists of an application that is designed to run in the hosted service and XML configuration files that define how the hosted service should run

A hosted service can have one or more Roles.

Now it comes to the Roles. Our cloud application can be a Web Based application, or a background processing application, or some legacy application which is hard to migrate. Or mix of the three. In order to make things easy for developers, Microsoft has defined 3 distinguished types of “Roles” – Web Role, Worker Role and VM Role. You can read a bit more for the “Role”s here. But the main idea is that a Role defines an application living environment. The Role contains all the code that our application consists of. It defines the environment where our application will live – how many CPUs will be installed; the amount of RAM installed; volume of local storages; will it be a full IIS or a background worker; will it be Windows Azure Guest OS 1.x or 2.x; will it has open ports for communication with outer world (i.e. tcp port 80 for Web Role); will it has some internal TCP ports open for internal communication between roles; what certificates will the environment has; environment variables; etc.

The Role is like a template for our cloud application. When we configure our Cloud Service (or Azure Hosted Service), we set the number of instances involved for each Role.

Instance is a single Virtual Machine (VM), which has all the properties defined by the Role and has our application code deployed. When I mentioned that the Role defines the number of CPUs, RAM, local storage, I was referring the configuration for each VM where our code will be deployed. There are couple (5) of predefined VM configuration which we can use:

And here comes the beauty of the Cloud. We code once. We set the overall parameters once. And we deploy once! If it comes that we need more servers – we just set the number of instances for our role. We do it live. There is no downtime. Windows Azure automatically will launch as many VMs as we requested. Will configure them for our application and will deploy our code in each and every one of them and will finally join them to the cluster of our highly available and reliable cloud application. When we don’t need (let’s say) 10 servers anymore, then we can easily instruct Windows Azure that we only need 2 from now on and that’s it. The cloud will automatically shutdown 8 servers and remove them, so we won’t be paying any more extra money.

It is important to note, though, that the Role defines the size of the VM for all the Instances of it. We cannot have instances of same Role but different VM size. This is by design. If we defined our Role to use Extra Large VM, then all the instances we have will be running on that size of VM.

Key takeaways

I hope that this article helped you understand couple of basic terms about Windows Azure. You shall be able to confidently answer the following questions:

Wednesday, December 14, 2011

Yeah, I know most of the DBAs (if not all) say to avoid using cursors in your SQL Server code, but there are still some things, which you can only achieve via cursors. You can read a lot discussions on whether to use cursors or not, is it good, is it bad.

My post is not about arguing what is good and what is bad. My post is about a tiny little option, which, if your logic allows you can use to optimize how your cursor works.

So we are using cursors, for good or bad. Everything might work just fine if we are using on-premise SQL Server, and if the server is not under heavy load. Our stored procedures, which are using cursors are executing in a matter of seconds. There is nothing unusual. We deploy our application to The Cloud. And of course we utilize SQL Azure as our DB backend. Now strange things begin happening. Our stored procedures crash with timeout exceptions. If we login to the server and use the good “sp_who3” (yes, this works in SQL Azure!) to see the processes running, we notice that some procedures do report a SOS_SCHEDULER_YIELD. You can read a lot of information on what does that mean. As by definition:

Occurs when a task voluntarily yields the scheduler for other tasks to execute. During this wait the task is waiting for its quantum to be renewed.

Most of the resources you will find explaining what does lot of SOS_SCHEDULER_YIELD mead, will suggest high CPU load, non-optimized queries, etc. But we look at our code and there is nothing unusual. Also, as this is SQL Azure, we can’t see the actual CPU load of the OS. We can’t add more CPU or more RAM. What do we do now ?

Well, review once again our cursor logic! If it is the case that we only read from the cursor’s data. We only read forward, never backward. We never change cursor’s data (update/delete). Then there is a pretty good chance that we can use the FAST_FORWARD keyword when declaring our cursors:

Specifies a FORWARD_ONLY, READ_ONLY cursor with performance optimizations enabled. FAST_FORWARD cannot be specified if SCROLL or FOR_UPDATE is also specified.

It is amazing performance booster and load relief! And we, most probably, will never see again the SOS_SCHEDULER_YIELD process status for our procedures.

Most (if not all) of the cursors I’ve written are never reading backward or updating data, so I pretty amazed to see the performance differences using this keyword. I for sure will use it from now on, whenever possible!.

Monday, December 5, 2011

It’s a great step toward proving that Microsoft is reliable cloud partner, to announce that Microsoft has passed ISO/IEC 27001:2005 certification. It is very strong information security certification which proves that our data is securely and reliably stored in the cloud.

You can find the official certificate on the certification authority’ website here. As you can read the scope of the certification is as follows:

The Information Security Management System for Microsoft Windows Azure including development, operations and support for the compute, storage (XStore), virtual network and virtual machines services, in accordance with Windows Azure ISMS statement of applicability dated September 28, 2011. The ISMS meets the criteria of ISO/IEC 27001:2005 ISMS requirements Standard.

Meaning that SQL Azure, CDN, ACS, Caching and Service Bus services are not yet covered by this certification. But I believe it is work in progress and very soon we will see update on that part. Yet, the most important part – where our code resides (Compute) and where our data live(storage) is covered.

Disclaimer

This is my personal blog space. Everything which I write here or anywhere on the web is solely my own subjective opinion and shall not be associated (neither affiliated) with any company - neither the company I currently work for, nor any company I have worked for in the past. Use the information and any code / links provided at your own risk.